the best parts to add for getting the best mpg when pulling?

i drive a 2006 2500HD 4x4 and pull a 36 and 32 ft. 5th wheel and other large trailers. ive added a k&n intake, hypertech programmer, and cherrybomb exhaust. what are other afterarket parts that will help increase my mpg?

Electric fans
full synthetic (oil, transmission, differentials)
Under drive and over drive pullys
headers
new spark plug wires with a greater thickness then stock
waxing your car and using a clay bar will help get rid of drag

Get rid of the hypertech and have you a custom tune made strictly for your truck and your mods. This will increase not only your pulling power but you gas mileage also. Off the shelf tuners are made to work on every truck. Custom tunes are made for your truck only. Also what kind of cherrybomb do you have and do you have any sound clips of it.

i have the dual exhaust system. im not sure if theres any more they call it but i busted the welds on the brackets for the pipes out the back so i put turn downs right behind the catiletic converter. y what does the sound clips do for me?

Look into the under drive pulleys, not a truck story but I feel it has a fair bit of value. I have a boat with a stroker motor, last spring I removed the belt driven sea water pump and installed a crank driven pump. I had to remove my crank shaft under drive pulley, the long and the short it coat me two MPH. Anyone who knows boat will tell you it takes a fair bit of HP for each mile added to top speed, going from a 4-1/2" pulley to a 6" pulley cost me dearly. I am having my under drive pulley machined to accept the crank driven pump to get my ponies back!!!! I am going to put a small pulley on my suburban next!!!

i familiar with cherrybombs, if your looking for mileage or power their not always the best option, an upgrade to a better size exhuast pipe and a muff with proper backpressure (but with low restiction, like a cherrybomb) would probably make a differnce, i think a pipe in the 2 and 3/4 inch range would be a good, set up, maybe go as big as three and a quarter if you plan on many modifications to help tow